The present invention relates to fiber-optic probes, in particular to fiber-optic probes for intravascular measurements comprising a fiber-optic core for conducting electro-magnetic radiation from a proximal end of said probe to a distal end of said probe and a sheath made of synthetic sheath material and disposed around said core. The present invention further relates to fiber-optic probe assembly comprising such a fiber-optic probe and an intravascular catheter, the latter comprising a probe lumen having a proximal opening and a distal opening and being adapted to accommodate said fiber-optic probe.
Fiber-optic probes of the kind initially mentioned are well-known from the prior art. An important application thereof is the optical in situ measurement of the oxygen saturation of blood, in particular of venous blood.
The centrovenous oxygen saturation (ScvO2) is of particular interest since valuable information about the oxygen availability and oxygen utilization of the entire organism can be obtained from it. A lowering of cardiac output, a reduction of the oxygen carrier hemoglobin, a reduced oxygen supply by artificial respiration or an uncompensated increase in the oxygen consumption of the organism can be quickly detected by continuously monitoring the centrovenous oxygen saturation, which thus is a cost-efficient, global physiological monitoring method. Usually, for centrovenous oxygen saturation in the flowing blood fiber-optic reflecto-oximetry at a measuring wavelength of about 660 nm. Optical radiation of another wavelength, e.g. 930 nm, is used as a reference wavelength. At this wavelength, there is no substantial difference between the reflection of oxygenated and oxygen-free hemoglobin. Parallel measurement at the reference wavelength serves the purpose of compensating flow-dependent and other artifacts.
Fiber-optic probes of the kind initially mentioned may also be used for liver function tests by means of fiber-optic reflection densitometry at a wavelength of about 805 nm after injecting indocyanine green (ICG). In this case, optical radiation at about 900 nm can be used as reference wavelength.
In the surgical field and in intensive medicine, centrovenous catheters (CVC) with several lumina, so-called multilumen CVC, are applied not only to serve for accommodating a fiber optic probe but also to measure the centrovenous pressure, supply infusion solutions, blood and blood derivatives as well as pharmaceuticals via lumnina, and take blood samples for hematological and biochemical analysis.
A catheter system for continuously measuring the centrovenous oxygen saturation is known from the U.S. Pat. No. 5,673,694. It describes a fiber-optic probe of the above type and a fiber-optic catheter with a continuous lumen extending parallel to the fiber-optic lumen for continuous cleansing of the fiber optic in the region of the distal tip. The catheter system has a flexibly adjustable length of the part of the fiber-optic probe inserted in a lumen of the already applied multilumen CVC. Since the fiber-optic probe can be flexibly advanced in its length by means of a frictionally connected locking device, the part of the fiber-optic probe or the fiber-optic catheter, respectively, situated outside of the multilumen CVC must be protected against bacterial contamination by means of a sterile cover.
U.S. Pat. No. 6,954,665 discloses a different way of connecting a fiber-optic probe of the type initially mentioned to a catheter. Therein, the probe is mounted to a Y-shaped connection piece at a fixed length of the probe. The Y-shaped connection piece is fixed to a proximal catheter port, e.g. using a Luer lock system, thus ensuring a predetermined position of the distal end of the probe relative to the catheter tip.
Generally, a small probe diameter is aimed for, as small probe diameters allow the probe lumen and thus the catheter to be designed with a smaller diameter as well in order to decrease the invasiveness of application. On the other hand, a smaller probe diameter usually results in a lower kink resistance. Further, the optical core usually contributes to mechanical stability of the probe to a higher degree than the sheath does, as the core fibers are made of a material stiffer as the sheath material. Therefore, for conventional probes of the above type it is common to provide a fiber-optic bundle to form the fiber-optic core, with multiple core fibers adding to the strength, but also to the diameter.